In an effort to monitor and control pollutants and other contaminants entering the environment from sources such as industrial facilities, governments have enacted regulations requiring these sources to collect samples from rainwater runoff. For example, the U.S. Environmental Protection Agency (EPA) has issued rules requiring the collection of water samples from storm events that cause accumulation greater than one inch in magnitude and which occur more than 72 hours from a prior storm event that required sample collection. Generally, the collected sample is required to contain storm water runoff occurring within the first 30 minutes of a storm event, often referred to as a “grab sample.” In addition to Federal regulations, many states have also established programs that require the collection of liquid samples prior to issuing permits to industrial facilities to allow them to discharge runoff into public storm drain systems.
To obtain a proper sample, a liquid collection system must be operable to collect the liquid at the onset of a storm event, and also to prevent the collection of debris or other contaminants prior to the storm event. The collection system must also be capable of stopping the collection of liquid after the 30 minute interval, otherwise undesirable dilution of the sample will occur.
Because the occurrence of storm events may be sporadic and unpredictable, it is impractical to have personnel standing by to place sample collection devices in position for the collection of liquid at the outset of a storm event. Accordingly, sampling systems have been developed which permit the automatic collection of storm water runoff without the need for human intervention. Many of these automatic collection systems include complex hardware and/or electronic monitoring equipment which are quite expensive. Other strictly mechanical systems capable of opening at the outset of a storm event are available, such as the device described in U.S. Pat. No. 5,821,437. However, these devices are also complex and thus quite costly. The financial burden that these prior storm water collection systems impose upon those who have need to use them has lead to a rather significant level of noncompliance with the government regulations. Furthermore, mechanical systems such as that described in U.S. Pat. No. 5,821,437 are susceptible to inadvertent triggering of the mechanism for opening the sample collection device prior to a storm event. While more simple systems for collecting storm water are available, these generally comprise open containers, often protected by only a grate to keep out large debris. These systems do not prevent the collection of unwanted debris which may pass through the grate and into the container prior to a storm event, and they do not prevent the accumulation of additional liquid after the grab sample has been obtained.
There is thus a need for a liquid sample collection system that overcomes drawbacks of the prior art such as those discussed above.